512 STRATIGRAPHICAL GEOLOGY 



2. Ireland and Scotland 



Ireland. Upper Cretaceous rocks appear nearly everywhere 

 round the edge of the great basaltic plateau of Antrim, Tyrone, 

 and Londonderry, and we may therefore safely infer that they 

 underlie the greater portion of it. It is also clear that they once 

 extended much farther westward than the present edge of that 

 plateau, as is proved by a small outlier near Draperstown. They 

 usually rest on a planed down surface of Liassic or Triassic rocks, 

 but sometimes overstep the limits of these, as in North-east Antrim, 

 and rest upon the Palseozoic rocks (see Fig. 186). 



These Irish Cretaceous rocks were described in 1865 by Pro- 

 fessor Tate, and an attempt to establish a zonal classification was 

 made by Dr. W. F. Hume in 1897, as shown in the following 

 table : 26 



Tate's Divisions. Hume's Zones. Feet. 



{( Zone of Belenmitella mucronata\ . ,, 

 5. White limestone ,, Actinocamax quadratus / 



[ ,, Actinocamax verus . . 3 to 5 



4. Chloritic Chalk = ,, Ecliinocorys gibbus . 3 to 4 



f3. Chloritic sands and flnoceramus zone (Upper Chalk) . 6 to 16 



sandstones \ZoneofExogyracolumba . . . 4 to 15 



\2. Yellow sandstones = ,, Ostrea carinata . . 4 to 30 



1. Glauconitic sands = ,, Exogyra conica . . . 4 to 16 



The glauconitic sands are regarded "by Dr. Hume as in part 

 equivalent to the Selbornian zone of Sch. rostratus, but the occur- 

 rence of Sch. variant, Pecten asper, and an Actinocamax like verus 

 (probably lanceolatus, Sow.) makes it difficult to accept this view. 

 The yellow sandstones contain layers of chert, and their fauna is a 

 curious mixture of Selbornian and Cenomanian forms, but as the 

 beds are shallow -water deposits it is probable that Selbornian 

 species here survived into Cenomanian time, and the occurrence of 

 Acanth. rotomagensis marks them as equivalents of Lower Chalk. 



The so-called Chloritic sands appear to include two deposits of 

 very different age, separated by a break and unconformity. The 

 lowest beds are calcareous glauconitic sandstones with Exogyra 

 columba, Pecten asper, and Trigonia crenulata, and are evidently of 

 late Cenomanian age. The higher glauconitic sandstones, as seen 

 north of Belfast and on the eastern coast, contain Spondylus 

 spinosus, Galerites conicus, Rhynchonella limbata, Rh. plicatilis, and 

 a species of Micraster with many broken Inocerami. These beds 

 pass up into a glauconitic sandstone, often pink in colour, which 

 yields Echinocorys vulgaris, var. gibbus, and a few other fossils. 



If the fossils are correctly identified these zones of Sp. spinosus 

 and Ech. gibbus must be regarded as a condensed representative of 



